Method of making fuse elements



1967 E. JACKS ETAL- METHOD OF MAKING FUSE ELEMENTS Filed July 13, 1964 United States Patent 3,358,363 METHOD OF MAKING FUSE ELEMENTS Eric Jacks, John Feenan, and Charles Frederick Leece, Liverpool, England, assignors to The English Electric Company Limited, London, England, a British company Filed July 13, 1964, Ser. No. 382,201 Claims priority, application Great Britain, July 19, 1963, 28,654/63 1 Claim. (Cl. 29-623) ABSTRACT OF THE DISCLOSURE This invention relates to a method of making fuse elements by preparing a photographic negative of the shape of the elements and exposing to light through the negative a strip of fusible metal covered with a light-sensitive material. The irradiated material is developed to render its exposed parts etch-resistant and an etch-resistant material is coated on to the unexposed (other) side of the strip to form a supporting layer there-for. Subsequently, the unexposed parts of the metal are etched away and the supporting layer is removed, leaving discrete fine etched fuse elements of the desired shape.

The invention relates to fuse elements.

According to the invention, a method of producing fuse elements includes the steps of applying in etchant-resistant material to the front surface of a strip or sheet of fusible metal an exact replica of the desired shape of the fuse element, the strip having the desired thickness of the fuse element, and applying to the back surface of the strip an etchant-resistant strip-supporting layer capable of being dissolved off by a suitable solvent, then applying etchant material to the front surface of the strip to etch away the strip except where etchant-resistant material has been applied to the front surface and, finally, dissolving off the strip-supporting layer so as to leave only the fuse element.

The carrying-out of the step of dissolving off the stripsupporting layer may be delayed until the fuse element is required for assembly in a fuse-link.

Preferably, the replica of the desired shape of the fuse element is applied to the front surface of the strip by preparing a photographic negative of the desired shape of fuse element, coating the front surface of the strip with light-sensitive material, exposing the coated front surface of the strip to light through the photographic negative so that an area of the light-sensitive material which is an exact replica of the desired shape of the fuse element is acted on by light passing through the photographic negative, developing the exposed coated front surface of the strip so as to harden and render etchantresistant the area of light-sensitive material acted on by the light, and removing the light-sensitive material not acted on by the light.

Advantageously, a plurality of spaced replicas of the desired shapes of fuse-elements are applied to the front surface of the strip in etchant-resistant material.

The invention also extends to include a fuse element made by the method set out in the preceding paragraphs.

One method according to the invention for making fuse elements will now be described by Way of example and with reference to the accompanying drawing which shows a plurality of fuse elements at an intermediate stage during manufacture.

The desired shape of a fuse element is drawn to a large scale on a relatively stable base material. The drawing is photographically reduced to normal size onto a stable base material such as a photographic glass plate or a photographic film, thus producing a negative of the 3,358,363 Patented Dec. 19, 1967 shape of the fuse element. From this negative, a number of photographic positives are prepared by contact printing and these are used to prepare a master negative comprising several negative reproductions of the shape of the fuse element arranged side by side.

Silver strip of suflicient width to produce the number of fuse elements reproduced on the master negative, and having the thickness required of the fuse elements, is prepared by cleaning it and coating one of its surfaces, referred to below as its front surface, with a light-sensitive material. The light-sensitive material is of a type which, when exposed to light and subsequently developed, becomes hard and resistant to an etchant solution, but unless exposed to light can be readily removed by washing.

The coated silver strip is then exposed to light through the master negative so that the light only acts on those areas of the strip aligned with the reproduction of the fuse elements on the master negative. The exposed strip is then developed and washed to remove the light-sensitive material not acted on by the light. The strip thus has imposed on it a positive image of exactly similar shape to the shape of the fuse elements on the master negative.

After drying, the back surface of the strip, that is, the surface not originally coated with light-sensitive material, is treated by applying to it an etchant-resistant layer of material which has sufficient strength to support the strip but which can be readily removed by immersing the strip in a suitable solvent. Examples of such material are solutions of the vinyl copolymer group such as Avigel (trademark).

The strip with the supporting layer is then immersed in the etchant solution which attacks the front surface of the strip and dissolves the silver except where it is covered by the hardened etchant-resistant light-sensitive material. The drawing shows the strip after this operation. The strip has been etched away to leave only portions 1, having the shape of the fuse elements, which are supported by the supporting layer 2. The fuse elements have thin neck-line parts 3 which help in providing the desired fuse characteristics, but which render the elements exceedingly weak structurally. The supporting layer 2, however, protects the elements from damage during the etching process and subsequently during handling.

When the elements are to be assembled into fuse-links, where they will be adequately supported, the supporting layer is dissolved off the strip by immersion in a suitable solvent such as trichloroethylene and the elements are thus separated ready for use.

What we claim as our invention and desire to secure by Letters Patent is:

A method of producing fuse elements from a sheet of silver foil comprising the steps of coating one side of the foil with a light-sensitive material,

positioning over the said side a photographic negative which defines a plurality of spaced replicas of the desired shape of each element,

irradiating with light the coated parts of said side which are uncovered by the negative,

developing the light-sensitive material whereby to harden and render etchant-resistant the light-irradiated parts of the said material, applying to the opposite side of the foil a hardenable etchant-resistant solution of the vinyl copolymer group so as to provide a supporting backing for the foil,

etching away from the said one side of the foil those parts thereof which have not been irradiated with light whereby to define spaced silver strip fusible elements of the desired shape, and

dissolving-away the supporting backing, this step being 2,735,763 2/ 1956 Heath 1568 X delayed .Whereby more .readily to permit'the han-- 3,079,352 2/ 1963 Atkins.

dling of the fuse elements prior to their assembly.

References Cited 5 UNITED STATES PATENTS CHARLIE T. MOON, Examiner.

332,286 12/ 18-85 Pfannkuche 200135 X J. L. CLINE, Assistant. Examiner JOHN F. CAMPBELL, Primary Examiner.

1,426,827 8/1922 Eustice. 

